This invention relates to eyeglass lenses for correcting color vision, which are capable of imparting the ability of discriminating normal color vision to color vision defectives having color blindness or color weakness.
Abnormal color vision includes congenital color vision defect and acquired color vision defect. The acquired abnormal color vision is caused as a result of diseases in the eyes or brain accompanied with other troubles, such as visual loss, strongly appearing in most cases. The congenital abnormal color vision depends solely on inheritance, and is usually called color blindness or color weakness. Any effective curing measure for the congenital color vision abnormality has never been found yet.
Optic cells in the eyes of human beings are classified into two types including optic rod cells and optic cone cells. The optic rod cells exhibit only sensitivity to brightness and darkness, and the optic cone cells serve to sensitize three light rays necessary for creating all color sensitization. The optic cone cells include three types, which are respectively called a red optic cone cell, a green optic cone cell and a blue optic cone cell when mentioned from a longer wavelength side. The three types of optic cells undergo the respective stimuli, and one is able to perceive a given color based on the combination in intensity of the stimuli.
A so-called "color vision defect" takes place due to either the incomplete abnormality or the absence of any of these three types of optic cells. The case where a trouble is involved in the red optic cone cells is called first abnormal color vision. Likewise, the case where a trouble results from the green optic cone cells is called second abnormal color vision, and the case where a trouble is involved in the blue optic cone cells is called third abnormal color vision. The third abnormal color vision is very rare in its frequency of appearance, thus presenting little problem thereon from the clinical standpoint.
The methods of rectifying abnormal color vision are disclosed, for example, in Japanese Laid-open Patent Application Nos. Sho.47-25990 and Sho.59-148027 and U.S. Pat. Nos. 4,300,819, 3,877,797 and 5,369,453. In Japanese Laid-open Patent Application No. Sho.47-25990, spectral characteristics effective for the rectification are not shown, so that if an absorption band in a dark vision is not imparted to, a complementary color with a long wavelength is particularly unlikely to be delivered to the optic nerve, thus making color recognition difficult. In Japanese Laid-open Patent Application No. Sho.59-148027 and U.S. Pat. No. 4,300,819, lenses, part of which is color(ed, are used so as to ensure the rectification by utilizing both the movements of eyes watching an object and an after-image. Moreover, in U.S. Pat. No. 3,877,797, the rectification is performed such that spectra emitted from a light-emitting object or reflecting object are altered through an optical filter prior to their arrival at eyes.
In U.S. Pat. No. 5,369,453, it is stated that as a result of computer resting of 300 patients of abnormal color vision, most of the color-blind viewers are able to discriminate three primary colors of red, green and blue in the trichromatic color vision system. They are merely appreciably poor in the ability of discriminating a color within a certain range of wavelength. The proportion of stimulation value of three kinds of optic cone cells is changed externally so that the proportion of the three kinds of optic cone cells being stimulated is caused to come closer to that of normal viewers, thereby ensuring the rectification of color blindness. Based on this, there can be obtained 4 types and 32 grades of color vision rectifying spectral characteristic curves and parameters. It has been found that color blindness can be classified into any of the 4 types and the 32 grades of color vision rectifying spectra. When a color-blind viewer wears eyeglasses, of which lenses exhibit color vision rectifying spectral characteristic curves corresponding to his/her color blindness, the color blindness can be properly rectified.
However, although the color vision rectifying theory is submitted in the U.S. Pat. No. 5,369,453, the lenses of color vision correcting eyeglasses are made only on an experimental basis, and there has never been proposed inexpensive and high-performance eyeglass lenses for color rectification which are serviceable on the market.
Among the four types of color vision rectifying spectral characteristic curves, there is a type wherein spectral changes are vigorous and light absorption has to be partly made at 100%. When using vacuum deposition (for partial reflection film) set out in the U.S. Pat. No. 5,369,453, it is difficult to make inexpensive, accurate lenses having prescribed color vision rectifying spectral characteristic curves. Especially, with plastic lenses whose demand has recently been great, limitation is placed on the type of constituent material for the vacuum deposition film. Thus, it is not easy to accurately convert all of the four types of color vision rectifying spectral characteristic curves into plastic eyeglass lenses.